Buggy code:
public class TransportHandlingSockJsService extends AbstractSockJsService implements SockJsServiceConfig { private static final boolean jackson2Present = ClassUtils . isPresent ( "com.fasterxml.jackson.databind.ObjectMapper" , TransportHandlingSockJsService . class . getClassLoader ( ) ) ; private final Map < TransportType , TransportHandler > handlers = new HashMap < TransportType , TransportHandler > ( ) ; private SockJsMessageCodec messageCodec ; private final List < HandshakeInterceptor > interceptors = new ArrayList < HandshakeInterceptor > ( ) ; private final Map < String , SockJsSession > sessions = new ConcurrentHashMap < String , SockJsSession > ( ) ; private ScheduledFuture < ? > sessionCleanupTask ; public TransportHandlingSockJsService ( TaskScheduler scheduler , TransportHandler ... handlers ) { } public TransportHandlingSockJsService ( TaskScheduler scheduler , Collection < TransportHandler > handlers ) { } public Map < TransportType , TransportHandler > getTransportHandlers ( ) { } public void setMessageCodec ( SockJsMessageCodec messageCodec ) { } public SockJsMessageCodec getMessageCodec ( ) { } public void setHandshakeInterceptors ( List < HandshakeInterceptor > interceptors ) { } public List < HandshakeInterceptor > getHandshakeInterceptors ( ) { } @ Override protected void handleRawWebSocketRequest ( ServerHttpRequest request , ServerHttpResponse response , WebSocketHandler handler ) throws IOException { } @ Override protected void handleTransportRequest ( ServerHttpRequest request , ServerHttpResponse response , WebSocketHandler handler , String sessionId , String transport ) throws SockJsException { TransportType transportType = TransportType . fromValue ( transport ) ; if ( transportType == null ) { if ( logger . isDebugEnabled ( ) ) { logger . debug ( ( "Unknown<seq2seq4repair_space>transport<seq2seq4repair_space>type:<seq2seq4repair_space>" + transportType ) ) ; } response . setStatusCode ( NOT_FOUND ) ; return ; } TransportHandler transportHandler = this . handlers . get ( transportType ) ; if ( transportHandler == null ) { logger . debug ( "Transport<seq2seq4repair_space>handler<seq2seq4repair_space>not<seq2seq4repair_space>found" ) ; response . setStatusCode ( NOT_FOUND ) ; return ; } HttpMethod supportedMethod = transportType . getHttpMethod ( ) ; if ( ! ( supportedMethod . equals ( request . getMethod ( ) ) ) ) { if ( ( OPTIONS . equals ( request . getMethod ( ) ) ) && ( transportType . supportsCors ( ) ) ) { response . setStatusCode ( NO_CONTENT ) ; addCorsHeaders ( request , response , OPTIONS , supportedMethod ) ; addCacheHeaders ( response ) ; } else if ( transportType . supportsCors ( ) ) { sendMethodNotAllowed ( response , supportedMethod , OPTIONS ) ; } else { sendMethodNotAllowed ( response , supportedMethod ) ; } return ; } HandshakeInterceptorChain chain = new HandshakeInterceptorChain ( this . interceptors , handler ) ; SockJsException failure = null ; try { SockJsSession session = this . sessions . get ( sessionId ) ; if ( session == null ) { if ( transportHandler instanceof SockJsSessionFactory ) { Map < String , Object > attributes = new HashMap < String , Object > ( ) ; if ( ! ( chain . applyBeforeHandshake ( request , response , attributes ) ) ) { return ; } SockJsSessionFactory sessionFactory = ( ( SockJsSessionFactory ) ( transportHandler ) ) ; session = createSockJsSession ( sessionId , sessionFactory , handler , attributes ) ; } else { response . setStatusCode ( NOT_FOUND ) ; <START_BUG> logger . warn ( "Session<seq2seq4repair_space>not<seq2seq4repair_space>found" ) ; <END_BUG> return ; } } if ( transportType . sendsNoCacheInstruction ( ) ) { addNoCacheHeaders ( response ) ; } if ( transportType . supportsCors ( ) ) { addCorsHeaders ( request , response ) ; } transportHandler . handleRequest ( request , response , handler , session ) ; chain . applyAfterHandshake ( request , response , null ) ; } catch ( SockJsException ex ) { failure = ex ; } catch ( Throwable ex ) { failure = new SockJsException ( ( "Uncaught<seq2seq4repair_space>failure<seq2seq4repair_space>for<seq2seq4repair_space>request<seq2seq4repair_space>" + ( request . getURI ( ) ) ) , sessionId , ex ) ; } finally { if ( failure != null ) { chain . applyAfterHandshake ( request , response , failure ) ; throw failure ; } } } private SockJsSession createSockJsSession ( String sessionId , SockJsSessionFactory sessionFactory , WebSocketHandler handler , Map < String , Object > attributes ) { } private void scheduleSessionTask ( ) { } }

Fix:
logger . warn ( ( "Session<seq2seq4repair_space>not<seq2seq4repair_space>found,<seq2seq4repair_space>sessionId=" + sessionId ) ) ;